The present invention relates in general to the field of hologram display and, more particularly, to a system and method for tracking a light source to illuminate a holographic display and to tracking sunlight to illuminate large scale holograms such as holographic billboard displays.
Holograms of any size generally have fixed optical illumination angles for best displaying characteristics such as brightness, spatial image fidelity and color fidelity. Moreover, it is generally preferable to illuminate holograms with light sources that approximate point light sources in order to achieve optimal image resolution. This is because light sources having extended sizes (e.g., incandescent light sources) tend to cause the blurring of image points in the hologram proportional to the size of the light source. Similarly, it is generally preferable to reduce and/or minimize the amount of diffuse light that illuminates a hologram. Consequently, hologram illumination schemes typically use single (or small numbers of) well controlled light sources that approximate point light sources, and contribute little to diffuse lighting of the hologram.
The need to tailor the location of the illumination source with respect to the hologram in order to have optical illumination angles for best displaying characteristics can, for example, be accomplished when an individual viewer can generally hold a small hologram and quickly adjust the illumination angle to establish an optimal viewing position relative to the available light source. The production of relatively large scale holograms is becoming more practical. The holograms typically have fixed positions, potentially unlimited size, and are intended for observation by multiple viewers. For such holograms, handheld manipulation and positioning is no longer a practical solution. Examples of techniques for one-step hologram production of potentially unlimited size holograms can be found in the U.S. Patent Application entitled xe2x80x9cMethod and Apparatus for Recording One-Step, Full-Color, Full-Parallax, Holographic Stereograms,xe2x80x9d Ser. No. 09/098,581, naming Michael A. Klug, Mark E. Holzbach, and Alejandro J. Ferdman as inventors, and filed on Jun. 17, 1998, which is hereby incorporated by reference herein in its entirety.
The aforementioned problems associated with optimal hologram display are additionally complicated when holograms are used for outdoor displays, and particularly large outdoor display (e.g., billboards) which are now possible due to the previously discussed advances in hologram production technology. The sun is a logical light source for illumination of outdoor holographic displays because sunlight is generally an extremely bright, efficient and low cost illumination source. However, the location of the sun, and thus angle at which the sun illuminates an outdoor holographic displays, changes throughout the day. Additionally, diffuse sunlight (e.g., sunlight scattered by clouds) illuminates outdoor holographic displays in an undesirable manner.
Accordingly, it is desirable to have a hologram illumination system optimized for illuminating outdoor holographic displays while still providing a desirable light source and illumination angle, and doing so efficiently and at low cost.
In accordance with teachings of the present disclosure, a system is described for illuminating a hologram such as a holographic billboard type display using the sun or other moving light source. One aspect of the present invention includes a system for illuminating relatively large scale holograms with a controlled angle beam of sunlight. Another aspect of the present invention includes using a heliostat to provide illumination from a moving light source for illumination of a hologram. For some applications an artificial light source may be combined with an optical tracking system incorporating teachings of the present invention to provide illumination when a sufficient amount of light from the moving light source is no longer available.
Technical benefits of the present invention including providing bottom illumination of a large scale hologram used in an outdoor display to avoid blurring of the associated image or images on cloudy days due to the effect of diffused light from the clouds. Bottom illumination of a large hologram used in an outdoor display is often more compatible with installation and positioning of an artificial light source relative to the hologram.
Accordingly, one aspect of the present invention provides a system for illumination of a hologram. The system includes at least one deflection mirror to direct light from a moving light source to illuminate the hologram, and a heliostat for tracking the moving light source and positioning the at least one deflection mirror to direct light therefrom to illuminate the hologram.